It is well established that delivery devices adapted for the delivery of dry powder medicaments suffer from the problem of contact with moisture. Such problems are particularly when hygroscopic medicaments are used or when climatic conditions give rise to high humidity. Medicament inhalers are known to suffer from such and moisture contamination of dry powder inhalers has long been held to be undesirable since the dry powder medicament may become clogged, creating problems in delivering correct dosages of medicament. Furthermore, some inhaled medicaments are themselves inherently moisture sensitive. Therefore, there has long been a desire to provide a dry powder inhaler that is resistant to moisture, that is, one that protects a medicament reservoir from moisture contamination either from the environment or from exhalation by a patient using the device and various attempts have been made to mitigate the problem.
Most attempts which have been made aim to reduce the moisture which comes into contact with a medicament, such attempts generally comprise the use of an additional chamber containing a desiccant.
International Patent Application No WO 98/41261 describes an inhalation device which includes a chamber for containing a desiccant, e.g. silica gel. Whilst the use of a desiccant gel does remove some moisture, the system is disadvantageous in that, inter alia, the leak paths are too great for the available desiccant to cope with and therefore the desiccant is only effective for a few hours, whereas there is a need for moisture resistance if at least a few months.
Similarly, International Patent Application No WO 96/08284 describes an inhaler system provided with a reservoir wherein the closed end of the reservoir is also provided with a desiccant cartridge.
International Patent Application No WO 95/32752 also describes a medicament chamber included in an inhalation apparatus and provided with a container containing a desiccant.
European Patent Application No. EP0520 440, Ambrosio et al, describes a dry powder inhaler which includes a moisture resistant barrier in the form of a flap which is designed to prevent exhaled air from a patient contaminating the medicament held in the reservoir.